The present invention relates generally to an optical sensor and, more particularly, to a reflection-type optical sensor having internal light reflection-promoting surfaces to provide improved detection capabilities.
As shown in FIGS. 7(a) and 7(b), a reflection-type optical sensor has been used as a sitting sensor for a toilet seat device A that can function also as a bidet. The optical sensor detects whether or not a person a is seated on the toilet seat b. The sitting sensor d is mounted to a fixture c to which the toilet seat b is mounted. The sitting sensor d has a light-emitting device such as an infrared diode or the like (not shown) that emits light toward the seated person a via a light-projecting lens. Light reflected by the seated person a is received by a light-receiving device such as a single position-sensitive device (PSD) via a light-receiving lens spaced from the light-emitting device by a given distance. Where the level of light received by the light-receiving device is smaller than a predetermined value, the sensor judges that no one is seated. Where the received light level exceeds the predetermined value, the sensor judges that a person is seated.
Where the result of the decision is that no person is seated, the device is controlled so that no water is ejected from a water nozzle even if a nozzle switch is depressed. Normally, the sitting sensor d is accommodated and held in a housing or holder (not shown). The holder is typically made of a dark synthetic resin such as a black-colored resin. The wall surface of the chamber through which passes light projected by the light-emitting device and light received by the light-receiving device pass is embossed. A cover e is swingably connected to the fixture c.
In the above-described prior art sitting sensor, a part of the light projected by the light-emitting device is absorbed into the holder and the amount of projected light decreases due to the color of the holder, the material of the holder, or the surface treatment of the holder wall surface. If the object (person a) to be detected is wearing clothing of low reflectivity, such as black-colored clothing, a part of the light is absorbed by the clothing due to its color. Therefore, a sufficient amount of reflected light cannot always be obtained. The reflected light is also absorbed by the holder, resulting in additional attenuation. Further attenuation is caused by the embossing of the chamber wall surface. As a result, adequate light may not reach the light-receiving device. Hence, detection is not properly performed. In this case, the result of the decision may be that no human is seated. That is, an erroneous decision occurs. Particularly in cases where the object (person a) to be detected is very close to the sensor, if reflection occurs at a short distance and the beam of the reflected light blurs, the aforementioned problem becomes even more conspicuous. This makes it impossible to detect a person in a seated state, which leads to an erroneous decision.
In view of the foregoing shortcomings, an object of the present invention is to provide a reflection-type sensor with improved detection capabilities.
To achieve the foregoing object, the present invention provides a reflection-type optical sensor comprising a light-projecting portion and a light-receiving portion formed in a holder, a light-projecting lens and a light-emitting device disposed in a light-projecting chamber formed in the light-projecting portion, and a light-receiving lens and a light-receiving device disposed in a light-receiving chamber formed in the light-receiving portion. The light-projecting chamber and the light-receiving chamber have wall surfaces that receive incident light and are light reflection-promoting surfaces for promoting the reflection of light. By providing light reflection-promoting surfaces, absorption of light projected by the light-emitting device into the holder and absorption of the reflected light into the holder is prevented; whereas attenuation would otherwise take place. Reflection of light incident on the reflection-promoting wall surface is promoted. This assures that light received by the light-receiving device is maximized. Hence, an erroneous decision is prevented.
Preferably, the above-described light reflection-promoting surfaces are formed as inner surfaces of the holder, and may comprise painted inner surfaces of the holder. These inner surfaces of the holder may also comprise inner surfaces of auxiliary members inserted in the holder.
The aforementioned light-receiving device is preferably a split type that makes a decision as to whether the object is remote or near, based on the position at which light is received and the amount of received light. This prevents an erroneous decision where the object is at a rather short distance.